My timber retaining wall is falling over, I'm just wondering what my options are? Is there a way to fix what I've got, or will I need to dig this whole area out and rebuild? You can't tell from the pictures but it's about 3-4 feet tall.

Not sure how/where that sprinkler head sprays, but it could be contributing to the erosion. This makes me suspect that there's not good drainage behind the wall, which likely is at least part of the reason the wall is tipping. When you rebuild the wall, make sure you include good drainage.
– Tester101Jul 13 '15 at 20:58

1

Please include a side shot. You're right...it's really impossible to judge the height here.
– DA01Jul 14 '15 at 0:51

I'm having a hard time figuring out why there is a retaining wall there in the first place. The pictures might be at a bad angle, but it looks like you can just remove the wall entirely and grade out the area by adding a lot of soil on the low side and smoothing it out. That would be a much cheaper option that replacing the wall.
– Jason HutchinsonJul 14 '15 at 18:51

@JasonHutchinson, thanks for the idea, I didn't even think about that. it's on my property line and was there when we moved in.
– Dan WilliamsJul 16 '15 at 14:55

Since it is on your property line, you will need to contact your neighbor to see who actually is responsible for the wall. Which side of the property is yours?
– Jason HutchinsonJul 16 '15 at 15:09

2 Answers
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It's quite hard to tell how big this wall is but you stated it's 3-4' tall.

It looks like it was built simply as a vertical wall. There's nothing you can do about it. It was inevitably going to tip over. So yes, you do have to dig it out.

If you want to replace it with timber, you need to add something called deadmen to it. A deadman is a timber that runs perpendicular to the wall itself that is then attached to another timber that runs parallel to the wall itself. Diagram:

Without those, your timber wall will always end up getting pushed over eventually.

The catch is, of course, to bury the deadman, you need to excavate all the dirt behind the wall back to about the same depth as the wall...so you'd be moving the 4' of dirt behind the wall as well. That may or may not work depending on who's side of the yard that is.

Another option is to go with a block wall. Retainer block walls are typically staggered backwards as it goes up. You then line the back side with drainable material (river rock) and a drain tile to allow any water building up a route of escape. However you're pushing the limits of most consumer-size retaining wall blocks at 4'.

Yet another option is to build two, 2' walls stepped back (one 2' wall on the bottom, then a second 2' wall several feet behind and above the first one). This is likely the best solution for long term retaining of the land. Plus it may offer some landscaping options (allow you to plant the strip in between with decorative plantings).

This is your best option. This is why the City I work for doesn't allow any walls over a certain height without a structural engineer. The step wall is the best option. Make it a landscaping feature with native plants that won't need a lot of water which will kill your wall. That drain pipe is helpful just make sure it has an outlet that is somehow on your property or permission from the neighbor so as to not start a fight.
– Dano0430Jul 14 '15 at 17:17

Wow, thanks for all the details. Much more than I was expecting :) As far as rebuilding it, will it make a difference if I wait for it to fall? Or will I just be making a bigger mess and a lot more work for myself.
– Dan WilliamsJul 16 '15 at 14:56

Classic example of a simple retaining wall built vertically - they ALWAYS fall over (except in the case of a LOT of permanent structure behind the face of the wall, making it more like one face of a box you can't see three sides of.)

You'll have to dig.

When you replace it, replace it with a wall that slopes, at least slightly, into the hill (ie, if it's 4 feet tall, the top should be 2.5-4 inches further left than the bottom, in this picture.) If you want to improve it further, also cut in 3-4 foot long timbers (if resusing the timbers or rebuilding it in timber) going into the dirt at the two foot level, every 6-8 feet. The goal is to make it VERY hard for the wall to be overturned. Sloping it puts the weight of the wall to work for you, rather than leaving it balanced between "dirt that wants to move" and "thin air" - you unbalance the wall to press against the dirt. Cross timbers add to the difficulty of turning the wall over by requiring a good deal of the dirt to lift up and tip over. That effect can be enhanced even more by fastening a buried timber parallel to the wall on top of the far ends of the cross timbers.